The present invention relates to a technique effective in an application to incorporating a voltage controlled oscillator (VCO) capable of switching an oscillation frequency into a semiconductor chip, specifically to a technique effective in use for a control loop of a transmission VCO in a high frequency semiconductor integrated circuit that modulates or up-converts a transmission signal, which is used in a radio communication device such as a mobile telephone capable of transmitting and receiving signals of plural bands.
There is a system called the GSM (Global System for Mobile Communication), which is used in the field of the radio communication device (mobile communication device) such as a mobile telephone, etc. This GSM system generally employs the phase modulation system called the GMSK (Gaussian Minimum Shift Keying) that shifts the phase of a carrier according to transmission data.
Now, in the recent mobile telephone of the GSM system, etc., a system called the EDGE (Enhanced Data Rates for GMS Evolution) has been used in practice in addition to the GMSK modulation mode. This new modulation system has the 3π/8 rotating8-PSK (phase shift keying) modulation mode that modulates the phase component and the amplitude component of a carrier. In contrast to the GMSK system that transmits information of one bit per one symbol, the 3π/8 rotating8-PSK (hereunder, called 8-PSK) modulation system is able to send information of 3 bits per one symbol. Thus, the EDGE mode is possible of a communication at a higher transmission rate (384K bps) in comparison to the GMSK mode.
As a means of realizing the modulation system that makes the phase component and the amplitude component of a transmission signal each carry information, there is a system called the polar loop, which is conventionally known. This system separates a transmission signal into the phase component and the amplitude component, and then applies feedbacks to the phase component and the amplitude component with a phase control loop and an amplitude control loop, respectively. Thereafter, an amplifier outputs to synthesize the above controlled signals (for example, Page 162, “High Linearity RF Amplifier Design” by Kenington, Peter B, Published by ARTECH HOUSE, Inc. 1979).
In recent years, in order to downsize the device and reduce the cost by decreasing the number of components in the radio communication system, many efforts and struggles have been made to incorporate as many circuits as possible into one or few semiconductor integrated circuits. As an example, there is a trial to incorporate a transmission oscillator into the semiconductor integrated circuit that possesses the modulation/demodulation function (hereunder, called RF IC). In regard to the RF IC for making up a communication system of the GSM system, the present applicant, etc. have developed and proposed the one that mounts a transmission oscillator on a semiconductor chip (Patent Document 1).
[Patent Document 1]
Ser. No. 10/373046, date of application to the US patent office: Feb. 26, 2003